Neutron transport in boiling media

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Copyright: Rothman, George Paul
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Abstract
The formulation of an adequate description of neutron populations in the presence of boiling moderator or coolant is attempted. Starting from a framework of comprehensive stochastic descriptions we concentrate on the special requirements of the boiling system such as the use of transport theory and the retention of heterogeneity in our model. Working equations are derived which show how adequate corrections for boiling can be made to the approximate models currently used. The detailed distribution of bubbles in a boiling system should be accounted for in accurate evaluations of criticality, especially where the bubbles are large. Evaluations of leakage, resonance escape probability and thermal absorption are modified by the detailed bubble distribution. Explicit corrections are given for simple examples, while inclusion of the effects into a practical criticality code, such as WIMS, is discussed. The second moments of the neutron population in the presence of boiling media are also described. The power spectral density arising from the fission process is evaluated, showing how this spectrum is affected by the boiling. Usually more important sources of neutron noise in a boiling reactor are the fluctuations in cross-sections and collision probabilities arising directly from random local void ages. This 'bubble noise' is evaluated with particular emphasis on the detection of onset of boiling in a channel or change in boiling regime. The use of Monte Carlo techniques in calculating neutron transport in boiling media is discussed in some detail. The applicability of the analyses of neutron means and variances to fast reactor situations is considered. The bulk of the work treats critical reactors. However, a treatment of transients and feedback effects is also included. A new analysis is suggested whereby means and variances throughout the transient can be evaluated without extreme difficulty. The concepts of stochastic stability are discussed.
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Author(s)
Rothman, George Paul
Supervisor(s)
Barrett, P.R.
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Publication Year
1972
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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download Rothman-006926134.pdf 10.69 MB Adobe Portable Document Format
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